The overall hypothesis is that the decline in physical activity habits and resultant increase in body fat reduces exercise capacity and muscle mass in military women. These lifestyle changes worsen metabolic and cardiovascular risk factors. Therefore, continued involvement in resistance and endurance exercise programs which increases or preserves fat-free mass, as well as enhances physical activity will prevent functional declines in military-eligible women. Although exercise is frequently recommended to enhance overall fitness, it is unclear as to whether endurance or resistance exercise is more effective in attenuating functional and cardiovascular declines in women. We will systematically compare the effects of endurance and resistance exercise on physical activity, cardiovascular fitness, and fat metabolism in military eligible women. To accomplish this objective military eligible women (18 to 35 yrs) will be randomized to a 6-month endurance training, resistance training or a control group. We will determine the effects of endurance training and resistance training on changes in: 1) free-living physical activity using doubly labeled water and indirect calorimetry; 2) body composition and body fat distribution using dual energy x-ray absorptiometry and computerized tomography, 3) in-vivo fat oxidation from 13Cpalmitate; and 5) insulin sensitivity from euglycemic clamps. Our results will provide new information on the energetic and physiological effects of endurance and resistance training on energy metabolism, cardiovascular fitness, and fuel utilization in women. We anticipate that the results from this study will provide the scientific basis for the recommended use of either endurance or resistance exercise as therapeutic modalities to increase physical activity, preserve fat-free mass, and decrease cardiovascular risk in military-eligible women. Between December 1996 and November we screened 72 women for this protocol. We invited for the overnight visit 56 volunteers and the same number entered the intervention period (exercise or control). By 11/30/1997 13 women were post-tested after the conclusion of the intervention period. During 1998, we plan to introduce 25 to 30 women to this protocol.